I agree with Smoothtalker - The circumstances surrounding the situation are as, if not more, important than the number of partners, of course age will also have a major impact. Theres a huge sifference between being 20 and having had 10 partners whereas someone who is 40 with the same number. Then again it is a good indicator of your lifestyle choices. Either way, the past can and usually is a good indicator of the future.
What I'd really like to know is the gender of the past partners